The present invention relates to the field of molecular biology, and more particularly, detection of single nucleotide polymorphisms, DNA sequence variation DNA mutations, DNA damage and DNA base pair mismatches. In particular, the invention relates to the use of DNA mutation binding proteins to detect single nucleotide polymorphisms, DNA sequence variations, DNA mutations, damaged DNA and DNA with mismatched base pairs.
Natural DNA sequence variation exists in identical genomic regions of DNA among individual members of a species. It is of interest to identify similarities and differences in such genomic regions of DNA because such information can help identify sequences involved in susceptibility to disease states as well as provide genetic information for characterization and analysis of genetic material.
When a cell undergoes reproduction, its DNA molecules are replicated and precise copies are passed on to its descendants. The linear base sequence of a DNA molecule is maintained during replication by complementary DNA base pairing. Occasionally, an incorrect base pairing does occur during DNA replication, which, after further replication of the new strand, results in a double-stranded DNA offspring with a sequence containing a heritable single base difference from that of the parent DNA molecule. Such heritable changes are called xe2x80x9cgenetic polymorphisms,xe2x80x9d xe2x80x9cgenetic mutations,xe2x80x9d xe2x80x9csingle base pair mutations,xe2x80x9d xe2x80x9cpoint mutationsxe2x80x9d or simply, xe2x80x9cDNA mismatchesxe2x80x9d. In addition to random mutations during DNA replication, organisms are constantly bombarded by endogenous and exogenous genotoxic agents which injure or damage DNA. Such DNA damage or injury can result in the formation of DNA mismatches or DNA mutations such as insertions or deletions.
The consequences of natural DNA sequence variation, DNA mutations, DNA mismatches and DNA damage range from negligible to lethal, depending on the location and effect of the sequence change in relation to the genetic information encoded by the DNA. In some instances, natural DNA sequence variation, DNA mutations, DNA mismatches and DNA damage can lead to cancer and other diseases of which early detection is critical for treatment.
There is thus a tremendous need to be able to rapidly identify differences in DNA sequences among individuals. In addition there is a need to identify DNA mutations, DNA mismatches and DNA damage to provide for early detection of cancer and other.
In order to meet these needs, the present invention concerns the use of proteins that function biologically to recognize DNA mutations to detect and map single nucleotide polymorphisms, DNA mutations, DNA mismatches and DNA damage.
In one embodiment, the present invention is directed to a method for detecting a DNA mutation in a DNA molecule comprising the steps of: (a) obtaining a solid support to which the DNA molecule is coupled; (b) forming a mixture by mixing the solid support (with DNA attached) and a labeled DNA mutation binding protein, the labeled DNA mutation binding protein being capable of detecting DNA mutations and binding to such mutated DNA; (c) forming a reacted sample by incubating the mixture under conditions wherein if the DNA molecule includes mutated DNA, the DNA damage binding protein binds to the mutated DNA; (d) analyzing the reacted sample by detecting the label on the solid support to detect the DNA mutation or absence thereof.
In another embodiment, the present invention is directed to a method for detecting a DNA mutation in a DNA molecule, said method comprising the steps of: (a) obtaining a solid support to which the DNA molecule is coupled wherein the DNA molecule is labeled; (b) forming a mixture by mixing the solid support (with labeled DNA attached) and a chimeric protein wherein the chimeric protein includes a DNA mutation binding protein and a nuclease and wherein the labeled DNA mutation binding protein is capable of detecting DNA mutations and binding to such mutated DNA; (c) forming a reacted sample by incubating the mixture under conditions wherein if the DNA molecule includes mutated DNA, the DNA damage binding protein binds to the mutated DNA and the nuclease cleaves the DNA thereby removing the label from DNA molecule coupled to said solid support and (d) analyzing the reacted sample by detecting the label or absence thereof on the solid support to detect the DNA mutation.
In another embodiment, the present invention is directed to a method of detecting a DNA mutation by a) obtaining a DNA molecule; b) coupling the DNA molecule to a flow cytometry bead to form a DNA-bead complex; c) forming a mixture by mixing the DNA-bead complex with a labeled DNA mutation binding protein; d) forming a reacted sample by incubating the mixture under conditions wherein if the DNA molecule includes mutated DNA the DNA mutation binding protein binds to the mutated DNA and e) analyzing the reacted sample by flow cytometry to determine the amount of label on the beads.
The present invention is also directed to a method for flow cytometric analysis to detect a DNA mutation in a DNA molecule by a) obtaining flow cytometry beads coupled to the DNA molecule; b) forming a mixture by mixing the beads and a labeled DNA mutation binding protein wherein the DNA mutation binding protein is capable of detecting DNA mutations and binding to such mutated DNA; c) forming a reacted sample by incubating said mixture under conditions wherein if the DNA molecule includes mutated DNA the DNA mutation binding protein binds to the mutated DNA; d) analyzing the reacted sample by flow cytometry to determine the amount of label on the bead; and e) detecting the DNA mutation or absence thereof by determining the amount of label on the beads.
In an alternative embodiment, the present invention is directed to a method for detecting a DNA mutation in a DNA molecule comprising the steps of: (a) obtaining a first DNA molecule; (b) coupling the first DNA molecule to a solid support to form a DNA-support complex; (c) obtaining a second DNA molecule; (d) forming a first mixture by mixing the second DNA molecule with the DNA-support complex; (e) incubating the first mixture under conditions such that the second DNA molecule hybridizes to the first DNA molecule thereby forming a hybrid double stranded DNA molecule coupled to the support wherein the hybrid DNA molecule includes one DNA strand from said the DNA molecule and one strand from the second DNA molecule; (f) obtaining a labeled DNA mutation binding protein, wherein the labeled DNA mutation binding protein is capable of detecting DNA mutations and binding to such mutated DNA; (g) forming a second mixture by mixing the labeled DNA mutation binding protein with the hybrid double stranded DNA molecule coupled to said support; (h) forming a reacted sample by incubating the second mixture under conditions wherein if the hybrid double stranded DNA molecule includes mutated DNA, the labeled DNA mutation binding protein binds to the mutated DNA and forms a labeled, hybrid double stranded DNA-support complex; (i) analyzing the reacted sample to detect the label or absence thereof on the hybrid double stranded DNA-support complex to thereby identify the DNA mutation.
The first DNA molecule may be coupled to the bead as single stranded DNA or as double stranded DNA and then converted to single stranded DNA by increasing the temperature or by placing the coupled DNA under conditions sufficiently stringent to convert the double stranded DNA to single stranded DNA. Similarly, the second DNA molecule may be added to the first mixture as single stranded DNA or as double stranded DNA and then converted to single stranded DNA by increasing the temperature or by placing the first mixture under conditions sufficiently stringent to convert the double stranded DNA to single stranded DNA.
In this embodiment, the nucleotide sequence of the first, single stranded DNA molecule may be known and the nucleotide sequence of said second, single stranded DNA molecule may be unknown. Where the first, single stranded DNA molecule is known the first DNA molecule may be wild type or mutant DNA and the second DNA molecule may be isolated from a host.
In an alternative format, the nucleotide sequence of the first DNA molecule may be unknown and the nucleotide sequence of the second DNA molecule may be known. Where the first DNA molecule is unknown the first single stranded DNA may be isolated from a host and the second DNA molecule may be wild type or mutant DNA.
In the method the DNA mutation may be a single nucleotide polymorphism in the first DNA molecule or the second DNA molecule or both DNA molecules.
In an alternative embodiment, the present invention is directed to a method for detecting DNA sequence variation between two DNA molecules comprising the steps of: (a) obtaining a first DNA molecule; (b) coupling the first DNA molecule to a solid support to form a DNA-support complex; (c) obtaining a second DNA molecule; (d) forming a first mixture by mixing the second DNA molecule with the DNA-support complex; (e) incubating the first mixture under conditions such that the second DNA molecule hybridizes to the first DNA molecule thereby forming a hybrid double stranded DNA molecule coupled to the support wherein the hybrid DNA molecule includes one DNA strand from said the DNA molecule and one strand from the second DNA molecule; (f) obtaining a labeled DNA mutation binding protein, wherein the labeled DNA mutation binding protein is capable of detecting DNA mutations and binding to such mutated DNA; (g) forming a second mixture by mixing the labeled DNA mutation binding protein with the hybrid double stranded DNA molecule coupled to said support; (h) forming a reacted sample by incubating the second mixture under conditions wherein if the hybrid double stranded DNA molecule includes mutated DNA, the labeled DNA mutation binding protein binds to the mutated DNA and forms a labeled, hybrid double stranded DNA-support complex; (i) analyzing the reacted sample to detect the label or absence thereof on the hybrid double stranded DNA-support complex to thereby identify the DNA mutation and detect the DNA sequence variation.
The DNA sequence variation may be a single nucleotide polymorphism.
The first DNA molecule may be coupled to the bead as single stranded DNA or as double stranded DNA and then converted to single stranded DNA by increasing the temperature or by placing the coupled DNA under conditions sufficiently stringent to convert the double stranded DNA to single stranded DNA. Similarly, the second DNA molecule may be added to the first mixture as single stranded DNA or as double stranded DNA and then converted to single stranded DNA by increasing the temperature or by placing the first mixture under conditions sufficiently stringent to convert the double stranded DNA to single stranded DNA.
In this embodiment, the nucleotide sequence of the first, single stranded DNA molecule may be known and the nucleotide sequence of said second, single stranded DNA molecule may be unknown. Where the first, single stranded DNA molecule is known the first DNA molecule may be wild type or mutant DNA and the second DNA molecule may be isolated from a host.
In an alternative format, the nucleotide sequence of the first DNA molecule may be unknown and the nucleotide sequence of the second DNA molecule may be known. Where the first DNA molecule is unknown the first single stranded DNA may be isolated from a host and the second DNA molecule may be wild type or mutant DNA.
In the methods of the invention, the host may be selected from the group consisting of humans, non-human animals, plants and microorganisms.
In the methods of the invention, the solid support may be a flow cytometry bead, a dipstick, a glass slide or a DNA chip. The label may be fluorescent, chemilluminescent or radioactive. In one embodiment the label is biotin. The DNA molecule may be a PCR product.
DNA mutation binding proteins which find use in the methods of the invention include human MutS homologue2 (hMSH2), xeroderma pigmentosum complementation group A (XPA), xeroderma pigmentosum complementation group C (XPC), xeroderma pigmentosum complementation group E (XPE), Thermus thermophilus Mut S (TthMutS), thymine DNA glycosylase (TDG), Escherechia coli Fpapy-DNA glycosylase, Escherechia coli endonuclease III, Escherechia coli exonuclease III, Escherechia coli endonuclease IV, T4 endonuclease, Escherechia coli uracil DNA glycosylase, Escherechia coli A/G-specific adenine DNA glycosylase (MutY), Escherechia coli Uvr A, Escherechia coli Uvr B and other DNA mutation binding proteins.
The DNA mutation binding proteins of the invention include those proteins having amino acid sequences depicted in SEQ ID NO:1, 3, 7, 9, 11, 15, 19, 21, 23, 25, 29, 31, 39, 35, 37, 101 and 103.
The DNA mutation binding proteins of the invention may be in the form of a chimeric protein. The chimeric proteins generally have sequences presented by the formulae: A-L-B and B-L-A wherein A is a peptide having DNA mutation binding activity and capable of binding to mutated DNA, B is a peptide having nuclease activity and L is a linker peptide. The chimeric proteins are linked in such a manner as to produce a single protein which retains the biological activity of both A and B.
Nucleases which find use in the chimeric proteins of the invention include the N-terminus of human excision repair cross-complementing rodent repair deficiency (XPF), Serratia marcescens nuclease, Escherechia coli Fpapy-DNA glycosylase; Escherechia coli endonuclease III; Escherechia coli endonuclease IV; T4 endonuclease; Escherechia coli uracil DNA glycosylase and Escherechia coil A/G-specific adenine DNA glycosylase, Escherechia coli Uvr B and Escherechia coli Uvr C.
The nucleases include those proteins having amino acids depicted in SEQ ID NO:5, 11, 13, 25, 31, 39, 35, 37, 103 and 105.
The linker peptide of the chimeric peptide of the invention generally consists of 8 amino acids rich in glycine and proline or other amino acids known to disrupt protein secondary structure. For example, the sequence GSGPSPGS (SEQ ID NO:17) finds use in the invention. However, in some circumstances the linker peptides will be as short as zero amino acids where the nuclease and DNA binding protein retain activity in the absence of a linker peptide. In other circumstances the peptide will have up to 5, 6,7, 8, 9 10, 11-15, 16-20 or 21-30 amino acids.